The invention relates to a metal contact member which is disposed at the bottom end of a measuring lance and onto which a consumable probe can be fitted to make an electrical connection, said probe containing measuring means for taking measurements in metal melts, the contact member consisting of two tubes interconnected by a tapered portion of one tube being pushed into the widened opening of the other tube with the interposition of an insulating member in the form of a sleeve, the outer wall portions of the two tubes abutting a flange of the insulating member having the same outside diameter as the contact member, and a cup-shaped insulating member being inserted into the widened interior of the end of the contact member which is electrically connected to the probe, the cup-shaped insulating member interior containing contacts which are insulated from one another and which are connected, through the base of the insulating member, to leads taken out through the contact member.
Measuring lances of this kind are used to determine oxygen activity and/or the temperature of steel melts. Incorrect measurements and divergent measurement results for which there was initially no explanation were found to occur in practice. Exhaustive experiments have shown that the falsification of the measurements is due to water inclusions present in the cardboard protective tubes surrounding the measuring probe and the contact member. On immersion of the probe into the melt the water is liberated and passes through capillary openings between the insulating members and the metal walls of the tubes of the contact member into its interior, which is filled with a filler. Since it is not possible to obtain perfect sealing between the filler and the metal tubes because of the different coefficients of thermal expansion of these parts, the penetrating moisture can, under unfavorable conditions, advance as far as the electrical contacts and falsify the measurements.
The present invention is based on the surprising finding referred to above, which has been confirmed by the experimental results. The object of the invention is so to devise and seal the contact member disposed on the measuring lance as to obviate falsification of the measurements due to penetrating moisture.
Starting from a metal contact member of the type described in the preamble, according to the invention, the sleeve-shaped insulating member is sealed from the wall of the widened portion of one tube and from the wall of the tapered portion of the other tube of the contact member and the cup-shaped insulating member is sealed from the wall of the widened interior of the tube end connected to the probe by the insertion of annular seals.